Answer
$$7.2 \times 10^{3} m$$
Work Step by Step
The time required for the woman to reach the water is:
Elapsed time$=\frac{d_{\text {woman}}}{v_{\text {woman}}}$
$==>$ Elapsed time $=\left(\frac{4.0 \mathrm{km}}{2.5 \mathrm{m} / \mathrm{s}}\right)\left(\frac{1000 \mathrm{m}}{1.0 \mathrm{km}}\right)$
$=>$ Elapsed time $=1600 \mathrm{s}$
In 1600 s, the dog travels a total distance of $d_{d o g}=v_{d o g} t$
$=>(4.5 m / s)(1600 s)=d_{d o g}$
$=>7.2 \times 10^{3} \mathrm{m}=d_{\mathrm{dog}}$
